This invention generally relates to wear resistant decorative laminates having excellent scratch, mar, scrape and abrasion resistance and methods of producing the same. More particularly, this invention relates to wear resistant, decorative laminates employing a decorative sheet saturated with a melamine-formaldehyde resin coating incorporating abrasive materials.
Conventionally, decorative laminates are made of two essential layers: a core layer and a surface layer. The core layer constitutes a bottom or supporting layer onto which the other layer is bonded. In normal high-pressure laminate manufacture, the core layer consists of a plurality of cellulosic sheets. The core sheets are generally made from a kraft paper impregnated with a laminating resin. Laminating resins commonly used for the core layer include phenolic, amino, epoxy, polyester, silicone, and diallyl phthalate resins to name a few. The industrially preferred laminating resin for decorative laminates is a phenolic resin made from the reaction of phenols with formaldehyde.
Placed above the core layer is a decorative layer which is generally an alpha cellulose pigmented paper containing a print, pattern design or solid color that has been impregnated with a melamine-formaldehyde resin.
The cured melamine-formaldehyde resins are colorless and resistant to light; they are resistant to a variety of solvents and stains; and their heat resistance make them resistant to burning cigarettes, boiling water and heated containers up to about 325.degree. F. Without these melamine-formaldehyde resins, the decorative laminate industry would not exist as it is known today. However, because these resins are extremely brittle, they sometimes require reinforcement.
When the decorative layer of the laminate is a printed pattern, it is covered with an overlay as it is commonly referred to, which is a high-quality alpha cellulose paper impregnated with a melamine-formaldehyde resin. This layer protects the decorative print from external abuse such as abrasive wear and tear, harsh chemicals, burns, spills and the like. It is primarily the melamine-formaldehyde resin which accounts for these protective properties. The alpha-cellulose paper acts as a translucent carrier for the water-thin resin, imparts strength to the rather brittle melamine-formaldehyde resin, maintains a uniform resin thickness in the overlay by acting as a shim, and controls resin flow.
The core layer, decorative layer and the overlay surface layer (when needed) are stacked in a superimposed relationship, between polished steel plates and subjected to a pressure and temperature for a time sufficiently long enough to cure the laminating resins impregnating the respective layers. The elevated temperature and pressure actually cause the impregnated resins within the sheets to flow, which consolidates the whole into an integral mass known as the laminate. These laminates are used as surfacings for counter tops, table tops, furniture, store fixtures and the like.
Abrasive materials have previously been employed in the overlay sheet or solid color decorative sheet in order to improve the abrasion resistance of the laminate. The abrasive materials are generally deposited upon the alpha cellulose matrix or, in other applications, mixed with cellulosic fibers or microcrystalline materials replacing the alpha cellulose overlay sheet.
Incorporation of abrasive materials in the decorative or overlay sheet can cause severe damage to the delicate, highly polished or intricately etched surfaces of the press plates when the abrasive particles deposited in the decorative or overlay sheet come into contact therewith.
Thus, there exists the need for substitution of a resin in the decorative or overlay sheet that will provide excellent surface damage resistance without damaging the delicate plates. Also incorporation of abrasive materials in laminates can cause objectional wear on materials rubbed across them. The provision for such a layer would fulfill a long-felt need and constitute a significant advance in the art.